# let z = Zed_rope.of_string @@ Zed_string.of_utf8 "abc" ;;
val z : Zed_rope.t = <abstr>
# let zip = Zed_rope.Zip.make_b z 0 ;; (* Still works *)
val zip : Z.t = <abstr>
# let zip = Zed_rope.Zip.make_b z 1 ;; (* Used to work before 2.0 *)
Exception: Zed_string.Out_of_bounds.
# let zip = Zed_rope.Zip.make_b z (-1) ;; (* Doesn't work either *)
Exception: Zed_rope.Out_of_bounds.